1. Field of the Invention
This present invention relates to histological and molecular pathology and more specifically to an immunohistochemistry staining system for staining tissue samples with a variety of chemicals to facilitate examination of the samples.
2. Description of the Related Art
Staining tissue with chemicals is generally well known in the field of molecular pathology. Tissue samples may be subjected to histological and molecular pathological tests including in-situ hybridization, polymerase, and to chemical stains which are commonly referred to as xe2x80x9cspecial stainsxe2x80x9d. A variety of chemicals may be used in the staining process, including biological reagents, antibodies, buffers, and deionized water. After a tissue is stained and rinsed with certain chemicals, one skilled in the art can identify the tissue type and any abnormalities in the tissue. Such methods may be used to identify various diseases in the tissue. Several methods of staining tissue are currently in use.
One conventional method utilizes capillary action in which a chemical in liquid state is drawn up a narrow space between two slides due to the attraction between the molecules of the chemical and the slides. One of the slides contains a tissue sample to be contacted with the chemical. An operator is generally required to pipette the appropriate staining chemicals into containers into which the slides are placed. Filling the containers tends to require a substantial amount of time. The slide pair is then manually or mechanically inserted vertically into each container in an order dependent on the type of chemical in each container. Manually placing the slide pair in the correct container may be difficult if the containers are not labeled for the appropriate chemical. The method may be also be difficult when performed mechanically if a mechanical arm is not properly programmed to move the slide pair sequentially to the proper containers. A computer may be used to program the movements of a mechanical arm. The of time that the slide pair is in each container is determined by using a watch or a computer.
Another method for staining tissue uses an automated dispensing head or nozzle to drop or spray chemicals onto a slide""s upper surface which contains the tissue sample. This may also be performed manually. An evaporation inhibitor is placed over the slide after a chemical agent is placed onto the tissue sample. The movable dispensing head draws the desired chemical from a container and dispenses the chemical on top of the appropriate slide. One limitation of this method is that a drop of liquid may form at the tip of the head after each dispensing operation and may drop onto another slide as the head moves. Also, the containers need to be filled with chemicals before they are dispensed, which requires labor. The length of time that elapses before each chemical is washed from a slide may be controlled by a computer.
A similar method involves dispensing a chemical from a dispenser pre-packaged with the chemical so that a person does not have to fill the dispenser. After each dispensing operation, the dispenser withdraws the drop remaining on the tip of its nozzle to prevent the drop from falling on a slide. The dispenser is placed in a rotating tray located above a slide tray. The tray moves the dispenser above the slide on which a chemical is dispensed. A computer is used to control the movement of the tray and to determine the length of time before a chemical is washed from a slide.
U.S. Pat. No. 5,232,664 relates to a dispenser for delivering small amounts of liquid to a sample. The dispenser includes a reservoir chamber linked to a dispense chamber. The dispense chamber communicates with a nozzle through an outlet line. A number of such dispensers are positionable within a reagent tray that is rotated by a drive carousel to perform an immunoassay. This patent and U.S. Pat. No. 5,595,707 are incorporated by reference as if fully set forth herein.
Turning to another method, chemicals may also be dispensed manually or from a mechanical transfer head into a gap between a cover plate and a slide containing a tissue sample. The slide and cover plate are in vertical positions. Gravity forces the chemicals through the gap. The surface tension between the slides prevents chemicals from flowing immediately out of the bottom of the gap. The transfer head may be filled with the appropriate chemical after each dispensing. Such a method requires significant time and labor. A computer may be used to control the movements of the transfer head and to time how long a slide is exposed to each chemical.
The methods presented above tend to be problematic. Some of the methods involve steps that are manually performed and require a significant amount of time. For example, an operator may be required to pipette a chemical onto a slide and/or fill chemical containers used for staining tissue. The operator may also have to carefully label these containers and time how long each chemical contacts the tissue. Such processes are labor-intensive and may be subject to significant variation due to human error. Further, some of the methods require the use of expensive automated equipment and a computer to control the equipment.
It is therefore desirable that an improved tissue staining system be derived which is less labor intensive. Further, it is desirable that the system requires less expensive equipment to stain the tissue. A system with these features would tend to increase the quality of the resulting stained tissue while reducing operating costs.
The problems outlined above are in large part solved by an improved tissue staining system and method of the present invention. That is, the system hereof does not require expensive equipment such as a computer in order to function. Further, the system may be automated such that less labor is needed to operate the system.
An embodiment of the system includes a cassette for housing the staining system. The cassette preferably has an open end into which a removable slide device may be placed. The slide device preferably includes a specimen slide for holding a tissue sample and a cover plate located above the specimen slide. A film is preferably located within the cassette for delivering one or more chemicals to the slide device. As described herein, a xe2x80x9cchemicalxe2x80x9d is taken to mean any substance added to the tissue sample to facilitate testing or examination of the tissue sample, including but not limited to a biological reagent, an antibody, a buffer, a label, a chromogen, a solvent, a resin and/or deionized water. Each chemical may be reactive or unreactive with the tissue sample.
The specimen slide and cover plate are preferably attached together in spaced relation to form a head space therebetween. A plastic (e.g., mylar) spacer may be placed between the cover plate and specimen slide. This spacer preferably creates the head space and preferably seals the outer edges of the slide device. The slide device may be held together with a slide holder. Alternately, the specimen slide and the cover plate may be constructed such that they can be snapped together to form a fixable engagement. On opposite ends of the slide device, an injection port and a relief port preferably communicate with the head space formed within the slide device. The injection port preferably includes a conduit, and that conduit preferably has a pointed end. A chemical may be passed through the injection port into the head space and then out of the head space through the relief port.
The slide device may be placed into the open end of the cassette. An injection piston preferably located within the cassette adjacent to the injection port may reciprocate in a direction toward the injection port. This reciprocating motion preferably enables the injection piston to contact containers disposed on the film. The containers contain one or more chemicals to be applied to the tissue sample, and holders may be used to attach the containers to the film. The film preferably extends along the edge of the cassette and forms a loop (e.g., in a horseshoe shape) in the interior of the cassette. Guide rollers within the cassette preferably move the film through the cassette such that the containers disposed within the film are passed to a location between the injection piston and the injection port.
The reciprocating motion of the injection piston is preferably synchronized with the movement of the film such that the piston contacts each holder of the film. In the case that a container is disposed within the holder contacted by the piston, the piston preferably forces the container against the pointed conduit end within the injection port. The pointed conduit end preferably punctures the container. The container preferably ruptures, causing the chemical(s) within the container to be released into the injection port. The piston preferably creates pressure within the injection port to cause the released chemical(s) to be positively displaced through the injection port and into the head space to stain the tissue sample. In the case that the head space contains a chemical that has been previously injected, such previously injected chemical is preferably displaced out of the head space by the pressure derived from the piston. The displaced waste chemical is preferably passed through the relief port and into a waste tank. The waste tank preferably contains absorbent material to facilitate collection of such waste chemicals.
The holders of the containers are preferably spaced apart by equal distances along the length of the film. The contact time between a chemical and a tissue sample is preferably determined by the distance between containers on the film. A specified number of holders may be left empty to create a predetermined amount of time between (a) the injection of a first chemical into the head space and (b) the injection of a second chemical into the head space and the simultaneous displacement of the first chemical from the head space. The motion of the film and the displacement of the injection piston are preferably synchronized such that each holder in the film is contacted by the injection piston.
The containers may hold more than one chemical. In an embodiment, two or more chemicals within the containers are separated by an interior wall within the container to prevent the chemicals from mixing before injection. When a container holding more than one chemical is forced against the pointed conduit end, each of the wall segments within the container is preferably punctured to allow the chemicals to mix before being injected into the slide device.
In an embodiment, the cassette may be placed onto a cassette driver for driving the guide rollers and the injection piston. The cassette driver preferably includes a shaft which may extend from the top of the cassette driver into the bottom of the cassette. The shaft is preferably a spline joint shaft which may be connected to the guide rollers and the piston. A gear drive motor preferably rotates the shaft at a constant speed, causing the guide rollers and the piston to move at a constant speed.
The cassette driver also preferably includes a heat pad and a thermostat for controlling the temperature of the chemicals in the head space of the slide device. The heat pad may be used to heat or cool the tissue sample and chemicals in the head space. The thermostat may maintain the heat pad within a predetermined temperature range or it may cause pulse changes in the temperature of the heat pad. In this way, the tissue and chemicals may be subjected to any pre-defined temperature profile. Maintaining the temperature of the tissue sample and chemicals within a selected range may facilitate or control reaction of the injected chemicals with the tissue sample. The cassette may be engaged with the cassette driver such that the heat pad is positioned under the slide device. The cassette driver preferably contains a pressure sensitive switch enabling automatic activation of the cassette driver motor when the cassette is detected on top of the cassette driver. A pre-set timing device may be used to stop the motor after a predetermined amount of chemicals have contacted the tissue sample.
In an embodiment, the tissue staining system includes a plurality of cassette drivers and a control panel for individually operating each of the cassette drivers. The control panel is preferably coupled to the motor and heat pad of each of the cassette drivers. A plurality of cassettes may be placed on the cassette drivers to allow a plurality of tissue samples to be stained simultaneously.
In an alternate embodiment, a portable cassette includes a battery operated solenoid piston for injecting chemicals into a slide device. The slide device is preferably located proximate the center of the cassette. The portable cassette preferably includes a twin drive motor for rotating guide rollers to move a film. The film preferably delivers containers to the solenoid piston. The portable cassette preferably includes a heat pad located under the slide device and a waste tank for collecting chemicals which are displaced from the slide device. The portable cassette may include printed contacts for activating the heat pad and/or the solenoid piston.
Each of the embodiments discussed above may be combined or used individually.
Further advantages of the present invention will become apparent to those skilled in the art with the benefit of the following detailed description of the preferred embodiments and upon reference to the accompanying drawings.